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Replacement Strategies (replacement + strategy)

Distribution by Scientific Domains

Medical Sciences	25%
Life Sciences	16%

Selected Abstracts

Comparison of Additional Costs for Several Replacement Strategies of Randomly Ageing Reinforced Concrete Pipes

COMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 7 2009
Franck Schoefs
Some of them carry seawater and can deteriorate with time because of internal corrosion. Because of the low O2 content of aggressive water, slow corrosion is expected for such applications. If the RCPs are not periodically replaced, they will eventually fail. Replacement strategies for these pipes depend on (1) the risks associated with the failure of the water distribution network, and (2) the costs associated with replacing the pipes, including the removal of existing pipes, installation of new pipes, and associated production losses. Because of the lack of statistical data regarding RCP failure, the development of a risk-based replacement strategy is not an easy task. This article demonstrates how predictive models for the evolution of the failure of RCPs and the associated consequences of failure can be used to develop risk-based replacement strategies for RCPs. An application for the replacement strategies of a network modeled as a system consisting of 228 RCPs is presented as a case study. We focus on the assessment of the number of replaced components that governs the costs. The main objective of this article is to provide a theoretical approach for comparing replacement strategies, based on (1) the results of a reliability study, (2) the representation of the distributions of failed components (binomial distribution), and (3) the decision tree representation for replacement of RCPs. A focus on the scatter of the induced costs themselves is suggested to emphasize the financial risk. [source]

Gene therapy as an alternative to liver transplantation

LIVER TRANSPLANTATION, Issue 12 2002
Betsy T. Kren
Liver transplantation has become a well-recognized therapy for hepatic failure resulting from acute or chronic liver disease. It also plays a role in the treatment of certain inborn errors of metabolism that do not directly injure the liver. In fact, the liver maintains a central role in many inherited and acquired genetic disorders. There has been a considerable effort to develop new and more effective gene therapy approaches, in part, to overcome the need for transplantation as well as the shortage of donor livers. Traditional gene therapy involves the delivery of a piece of DNA to replace the faulty gene. More recently, there has been a growing interest in the use of gene repair to correct certain genetic defects. In fact, targeted gene repair has many advantages over conventional replacement strategies. In this review, we will describe a variety of viral and nonviral strategies that are now available to the liver. The ever-growing list includes viral vectors, antisense and ribozyme technology, and the Sleeping Beauty transposon system. In addition, targeted gene repair with RNA/DNA oligonucleotides, small-fragment homologous replacement, and triplex-forming and single-stranded oligonucleotides is a long-awaited and potentially exciting approach. Although each method uses different mechanisms for gene repair and therapy, they all share a basic requirement for the efficient delivery of DNA. [source]

Impaired bioavailability of vitamin A in adults and children with persistent diarrhoea in Zambia

ALIMENTARY PHARMACOLOGY & THERAPEUTICS, Issue 7 2001
P. Kelly
Background: We have previously demonstrated a strong relationship between low serum retinol concentration and mortality in Zambian AIDS patients with diarrhoea, but were unable to detect any benefit from oral micronutrient supplementation. Aim: To test the hypothesis that this is related to impaired availability of vitamin A, we analysed serum retinol concentration changes over 6 h following oral mega-dose therapy (60, 120 or 180 mg retinol). Methods: Twenty-four men without diarrhoea, 15 adults with persistent diarrhoea and 11 children (six girls, five boys) with persistent diarrhoea were studied. Results: Men with persistent diarrhoea had lower baseline serum retinol concentrations (median 0.39 ,mol/L, interquartile range 0.21,0.56) than controls (median 1.16 ,mol/L, interquartile range 0.84,1.47; P=0.0003). After 60 mg retinol, the rise in serum retinol in HIV seropositive controls (median 0.63 ,mol/L, interquartile range 0.35,0.77) did not differ significantly from that observed in HIV seronegative controls (median 0.35 ,mol/L, interquartile range , 0.04,0.56; P=0.20). Increasing the dose to 120 mg or 180 mg retinol did not enhance the increase in serum retinol concentration. The increase in serum retinol was less in adults with persistent diarrhoea (median 0.25 ,mol/L, interquartile range 0.04,0.35) and in children (median 0.11 ,mol/L, interquartile range 0.04,0.46) than in men without diarrhoea (median 0.44 ,mol/L, interquartile range 0.26,0.74; P=0.03). Adults and children with diarrhoea had greater losses of retinol in urine over a 24-h period than controls, but less than 1% of the ingested dose was excreted. Conclusions: These results suggest that persistent diarrhoea in this population is associated with reduced bioavailability of retinol. Further work is required to determine the metabolic fate of therapeutic doses of retinol and to determine appropriate replacement strategies for HIV infected individuals. [source]

Human neural stem cell grafts in the spinal cord of SOD1 transgenic rats: Differentiation and structural integration into the segmental motor circuitry

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 4 2009
Leyan Xu
Abstract Cell replacement strategies for degenerative and traumatic diseases of the nervous system depend on the functional integration of grafted cells into host neural circuitry, a condition necessary for the propagation of physiological signals and, perhaps, targeting of trophic support to injured neurons. We have recently shown that human neural stem cell (NSC) grafts ameliorate motor neuron disease in SOD1 transgenic rodents. Here we study structural aspects of integration of neuronally differentiated human NSCs in the motor circuitry of SOD1 G93A rats. Human NSCs were grafted into the lumbar protuberance of 8-week-old SOD1 G93A rats; the results were compared to those on control Sprague-Dawley rats. Using pre-embedding immuno-electron microscopy, we found human synaptophysin (+) terminals contacting the perikarya and proximal dendrites of host , motor neurons. Synaptophysin (+) terminals had well-formed synaptic vesicles and were associated with membrane specializations primarily in the form of symmetrical synapses. To analyze the anatomy of motor circuits engaging differentiated NSCs, we injected the retrograde transneuronal tracer Bartha-pseudorabies virus (PRV) or the retrograde marker cholera toxin B (CTB) into the gastrocnemius muscle/sciatic nerve of SOD1 rats before disease onset and also into control rats. With this tracing, NSC-derived neurons were labeled with PRV but not CTB, a pattern suggesting that PRV entered NSC-derived neurons via transneuronal transfer from host motor neurons but not via direct transport from the host musculature. Our results indicate an advanced degree of structural integration, via functional synapses, of differentiated human NSCs into the segmental motor circuitry of SOD1-G93A rats. J. Comp. Neurol. 514:297,309, 2009. © 2009 Wiley-Liss, Inc. [source]

Optimal replacement policy for obsolete components with general failure rates

APPLIED STOCHASTIC MODELS IN BUSINESS AND INDUSTRY, Issue 3 2008
Sophie MercierArticle first published online: 8 JAN 200
Abstract Identical components are considered, which become obsolete once new-type ones are available, more reliable and less energy consuming. We envision different possible replacement strategies for the old-type components by the new-type ones: either purely preventive, where all old-type components are replaced as soon as the new-type ones are available; either purely corrective, where the old-type ones are replaced by new-type ones only at failure; or a mixture of both strategies, where the old-type ones are first replaced at failure by new-type ones and next simultaneously preventively replaced after a fixed number of failed old-type components. To evaluate the respective value of each possible strategy, a cost function is considered, which represents the mean total cost on some finite time interval [0, t]. This function takes into account replacement costs, with economical dependence between simultaneous replacements, and also some energy consumption (and/or production) cost, with a constant rate per unit time. A full analytical expression is provided for the cost function induced by each possible replacement strategy. The optimal strategy is derived in long-time run. Numerical experiments conclude the paper. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Comparison of Additional Costs for Several Replacement Strategies of Randomly Ageing Reinforced Concrete Pipes

Neural stem cells for the treatment of disorders of the enteric nervous system: Strategies and challenges

DEVELOPMENTAL DYNAMICS, Issue 1 2007
Maria-Adelaide Micci
Abstract The main goal of this review is to summarize the status of the research in the field of stem cells transplantation, as it is applicable to the treatment of gastrointestinal motility. This field of research has advanced tremendously in the past 10 years, and recent data produced in our laboratories as well as others is contributing to the excitement on the use of neural stem cells (NSC) as a valuable therapeutic approach for disorders of the enteric nervous system characterized by a loss of critical neuronal subpopulations. There are several sources of NSC, and here we describe therapeutic strategies for NSC transplantation in the gut. These include using NSC as a relatively nonspecific cellular replacement strategy in conditions where large populations of neurons or their subsets are missing or destroyed. As with many other recent "breakthroughs" stem cell therapy may eventually prove to be overrated. However, at the present time, it does appear to provide the hope for a true cure for many currently intractable diseases of both the central and the peripheral nervous system. Certainly more extensive research is needed in this field. We hope that our review will encourage new investigators in entering this field of research ad contribute to our knowledge of the potentials of NSC and other cells for the treatment of gastrointestinal dysmotility. Developmental Dynamics 236:33,43, 2007. © 2006 Wiley-Liss, Inc. [source]

Clinical Judgment Versus Decision Analysis for Managing Device Advisories

PACING AND CLINICAL ELECTROPHYSIOLOGY, Issue 10 2008
MITESH S. AMIN M.D.
Introduction: Implantable cardioverter-defibrillator (ICD) and pacemaker (PM) advisories may have a significant impact on patient management. Surveys of clinical practice have shown a great deal of variability in patient management after a device advisory. We compared our management of consecutive patients in a single large university practice with device advisories to the "best" patient management strategy predicted by a decision analysis model. Methods: We performed a retrospective review of all patients who had implanted devices affected by an advisory at our medical center between March 2005 and May 2006 and compared our actual patient management strategy with that subsequently predicted by a decision analysis model. Results: Over 14 months, 11 advisories from three different manufacturers affected 436 patients. Twelve patients (2.8%) were deceased and 39 patients (8.9%) were followed at outside facilities. Management of the 385 remaining patients varied based on type of malfunction or potential malfunction, manufacturer recommendations, device dependency, and patient or physician preferences. Management consisted of the following: 57 device replacements (15.2%), 44 devices reprogrammed or magnets issued (11.7%), and 268 patients underwent more frequent follow-up (71.3%). No major complications, related to device malfunction or device replacement, occurred among any patient affected with a device advisory. Concordance between the decision analysis model and our management strategy occurred in 57.1% of cases and 25 devices were replaced when it was not the preferred treatment strategy predicted by the decision model (43.9%, 37.3% when excluding devices replaced based on patient preference). The decision analysis favored replacement for all patients with PM dependency, but only for four patients with ICDs for secondary prevention. No devices were left implanted that the decision analysis model predicted should have been replaced. Conclusions: We found that despite a fairly conservative device replacement strategy for advisories, we still replaced more devices when it was not the preferred device management strategy predicted by a decision analysis model. This study demonstrates that even when risks and benefits are being considered by experienced clinicians, a formal decision analysis can help to develop a systematic evidence based approach and potentially avoid unnecessary procedures. [source]